Magnetic circuits for magnetrons



March 15, 1955 CLAMPITT ET AL 2,704,333

MAGNETIC CIRCUITS FOR MAGNETRONS Filed Jan. 27, 1954 2 Sheets-Sheet l FREDERICK B. PAR/ 5" INVENTORs LAWRENCE L. CLAMP/T7 ATTORNEY March 1955 L. CLAMPITT ET AL 2,704,333

MAGNETIC CIRCUITS FOR MAGNETRONS Filed Jan. 27, 1954 2 Sheets-Sheet. 2

/NVEN TOP LAWRENCE L. CLAMP/T7 FREDERICK 5. PA r v s ATTORNEY United States Patent MAGNETIC CIRCUITS FOR MAGNETRONS Lawrence L. Clampitt, Needham, and Frederick B. Parks,

Winchester, Mass., assignors to Raytheon Manufacturing Company, Waltham, Mass., a corporation of Delaware Application January 27, 1954, Serial No. 406,556

3 Claims. (Cl. 31539.61)

This invention relates to the magnetic circuit of magnetrons. In tunable magnetrons of the Cookie Cutter or Crown of Thorns type where a piece of nonmagnetic material is inserted varying distances into one or more anode cavities of the magnetron through a diaphragm or bellows and one pole piece of the magnetic circuit, the presence of varying amounts of magnetic material in the magnetic circuit as the anode is tuned varies the intensity and distribution of the magnetic field in the region between the cathode and the anode. This variation in the magnetic field effects the performance of the magnetron. Positioning the pole pieces clear of the movement of the tuning structure results in a large gap in the magnetic circuit and requires a larger magnet. It is the purpose of this invention to so construct the pole piece and the tuning structure as to maintain, as nearly as possible, a constant amount of magnetic material in the magnetic circuit throughout the range of movement of the tuning structure and to do this with a minimum magnetic gap, so as to minimize the size of the magnet. This is accomplished by positioning a piece of magnetic material close to the cathode-anode space and extending the movable portion of the pole piece that supports and moves the tuning structure into the region of the added piece so that a considerable area of both pieces are in juxtaposition at every position of the tuning structure so that the variation of the reluctance of the magnetic circuit is kept to a minimum and the gap between pole pieces is kept to a minimum.

Other and further advantages of this invention will be apparent as the description thereof proceeds, reference being had to the accompanying drawings wherein:

Fig. 1 is a sectional view of a magnetron utilizing a preferred embodiment of the invention;

Fig. 2 is a section taken along the line 2-2 of Fig. 1;

Fig. 3 is a sectional view of a magnetron utilizing another embodiment of the invention; and

Fig. 4 is a section taken along the line 44 of Fig. 3.

In Figs. 1 and 2, the reference numeral designates the anode supporting ring of conductive material, such as copper, of a magnetron to which are attached radial vanes 11 also of conductive material. Recesses 12 are formed in these vanes into which an annular tuning element 13 of conductive non-magnetic material fits. This tuning element 13 is supported on a ring 14, also of nonmagnetic conductive material, by means of mounting lugs 13a. The ring 14 is, in turn, attached to a plunger rod 15 of magnetic material such as steel that is positioned within an opening in a pole piece 16 of magnetic material that is fit in an opening in a cover plate 17 of conductive material. A second cover plate 18, also of conductive material, covers the top of the anode cavity and supports a second pole piece 20 of magnetic material that, in turn, supports, within an opening 21, a cathode 22 that may be of any of the types used for tubes of this type. The outer end of the rod 15 is threaded in the region 23 as is also the interior of the pole piece 16 in the region 24. The pitch of the thread in these regions 23 and 24 is made different to cause relative movement between the pieces 15 and 16 when the piece 25 is rotated. A cylindrical piece 25 has threads 26 on its outer surface to engage the threaded region 24 on the pole piece 16. The inner surface of this piece 25 also has threads 27 to engage the threads 23 of the rod 15. The inner end of the rod 15 is somewhat enlarged and formed with an opening 28 dimensioned to receive a rod 29 of magnetic material supported directly under the cathode-anode region by a disk 30 on non-magnetic material formed with supports 30a to permit the passage of the mounting lugs 13a of the tuning element 13. A flexible diaphragm 31 is fastened to supporting ring 14 and the lower cover plate 17 to permit movement of the tuning element without destroying the vacuum within the cavity.

In operation, as the cylindrical piece 25 is rotated in one direction, the rod 15 is raised to envelop the rod 29 and carries with it the tuning element 13 that penetrates into the recess 12 in the vanes 11. When the cylindrical piece 25 is rotated in the opposite direction, the rod 15 recedes from about the rod 29 but never entirely leaves it. In this position the tuning element 13 is fully retractive from the recess 12 in the vanes 11, but it will be seen that there is still a considerable area of the rod 15 and the rod 29 in juxtaposition. It will be seen that the magnetic circuit flows from the magnet (not shown) through the pole piece 16, the plunger rod 15, the rod 29 and the upper pole piece 20 back to the magnet. Due to the rod 29 and the opening 28 in the plunger 15 this circuit is never entirely broken. Thus, there is no substantial change in the magnetic circuit between the fully extended and fully retracted positions of the tuning element 13.

A modification of this invention is shown in Figs. 3

and 4. This modification may be somewhat easier to construct, but is not quite as effective as the construction shown in Figs. 1 and 2. The anode supporting ring supports a plurality of radial vanes 41. These vanes, as before, are formed with recesses 42 into which an annular tuning element 43 of non-magnetic conductive material fits. This element 43 is supported on a ring 44, also of non-magnetic conductive material, by means of supporting lugs 43a. This ring 44 is in turn attached to a plunger 45 of magnetic material that is positioned within a cylindrical pole piece 46 of magnetic material that is set in an opening in a cover plate 47 of conductive material. A second cover plate 48, also of conductive material, covers the top of the anode cavity and supports a second pole piece 50 of magnetic material that in turn supports, within an opening 51, a cathode 52. This cathode and its mounting may be of any of the well-known types used in magnetrons. A driving structure for the rod 45 similar to that shown in Fig. 1 is used. A cylindrical piece 53 of magnetic material is mounted concentric with the plunger 45 directly below the cathode-anode space by means of a disk 54 formed with slots 55 to receive the mounting lugs 43a of the tuning element 43. The disk 54 is attached to the lower plate 47. The anode space is kept vacuum tight by a diaphragm 56 that is attached to a piece 47a connecting the ring 40 and the cover plate 47 and to the ring 44. In operation, as the tuning element 43 is projected into the recesses 42, plunger 45 penetrates into the inte- 1101' of the cylinder 53 as shown in the right-hand side of Fig. 3. As the tuning element 43 is retracted from the recess 42, the plunger 45 retracts from within the cylinder 53 but never entirely leaves it. Thus the magnetic circuit from the magnet through the lower pole piece 46, the plunger 45, the piece 53 and the upper pole piece 50 back to the magnet is never completely broken throughout the range of movement of the tuning element 43.

Two embodiments of the invention have been illustrated and described. It is to be understood that details of the construction of the magnetron in which the invention is used may be altered. The invention may be used with the other types of mechanical tuning structures for magnetrons.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A tunable electron discharge device comprising a cathode, an anode structure formed with resonant cavities,

means for producing a magnetic flux in a direction at right angles to a plane including the openings to the cavity resonators, and tuning means for at least one of the cavities of said anode comprising conductive elements adapted to be inserted in said cavities and means for controlling the degree of insertion of said elements into said cavity, said magnetic flux providing means comprising pole pieces of-magnetic material positioned on either side of the resonant cavity openings, one of said pole pieces comprising an external part formed with an opening to receive a second part adapted for movement with the tuning element, means for moving the second portion relative to the first, and a third piece positioned near the space between the anode and the cathode and shaped and located in a manner to present a considerable area in juxtaposition to the second part throughout its motion.

2. A tunable electron discharge device comprising a cathode, an anode structure formed with resonant cavities, means for producing a magnetic flux in a direction at right angles to a plane including the openings to the cavity resonators, and tuning means for at least one of the cavities of said anode comprising conductive elements adapted to be inserted in said cavities and means for controlling the degree of insertion of said elements into said cavity, said magnetic flux providing means comprising pole pieces of magnetic material positioned on either side of the plane of the resonant cavity openings, one of said pole pieces comprising an external part formed with an opening to receive a second part adapted for movement with the tuning element, said second part formed with a recess, means for moving the second portion relative to the first, and a third piece positioned near the space between the anode and the cathode and shaped and located in a manner to fit within the recess in the second piece and present a considerable area in juxtaposition to the second part throughout its motion.

3. A tunable electron discharge device comprising a cathode, an anode structure formed with resonant cavities, means for producing a magnetic flux in a direction at right angles to a plane including the openings to the cavity resonators, and tuning means for at least one of the cavities of said anode comprising conductive elements adapted to be inserted in said cavities and means for controlling the degree of insertion of said elements into said cavity, and magnetic flux producing means comprising pole pieces of magnetic material positioned on either side of the plane of the resonant cavity openings, one of said pole pieces comprising an external part formed with an opening to receive a second part adapted for movement with the tuning element, means for moving the second portion relative to the first, and a tubular third piece positioned near the space between the anode and the cathode and shaped and located in a manner to permit the insertion of the second piece and present a considerable area in juxtaposition to the second part throughout its motion.

Nelson Feb. 7, 1950 Brown May 30, 1950 

